Date: Thu, 9 May 2002 22:39:30 +0200 From: Daniel Lang <dl@leo.org> To: freebsd-net@freebsd.org Subject: Multiple NICs on the same subnet Message-ID: <20020509203930.GA32900@atrbg11.informatik.tu-muenchen.de>
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Hi,
I want to use multiple NICs on the same subnet.
Thats my setup:
FreeBSD 4.5-STABLE (updated 2-3 weeks ago, no 4.6-PRERELEASE yet),
3 NICs inside: 2 x 3com 905C-TX, 1 x D-Link DGE-500SX (Level 1
Gigabit).
Now I want to assign a couple of IP addresses to those NICs. All
IP addresses are on the same subnet, and they correspond to different
kind of services available from this host, like FTP, CVSup, http,
rsync, etc.
Previously all services have been served by a single NIC, and I've
used IP aliases to assign the service bound addresses to the
NIC. Now I want to assign a certain set of services to different NICs
(which all have separate uplinks at their switches and thus can
achieve more bandwidth), like bind the FTP service to the
lge interface, and maybe rsync and CVSup to one of the 3coms
and the rest to the remaining 3com.
This does not seem to be possible. If I want to assign an address
to one of those NICs, I get an error from an ioctl like
"file exists". Reading the archives, etc, it seems like I need
to assign this address as an alias. This sort of worked. I could
assign an address to one of the other NICs by choosing a
netmask of /32 and stating alias on using ifconfig. But, our
switch did not register any packets from one of the other NICs
other than the default interface (one of the 3coms). It seems, like
the address may be assigned to one of the NICs, but even
if I use an application which explicitly binds to a certain
source IP, the packet does not get sent by the interface, which has
this IP address assigned, but by the default interface.
This would not be that much of a problem so far.
The problem really showed up, when it seemed like the
Gigabit interface did not seem to work as expected.
A couple of possible problems may be the cause, symptoms
beeing "lge0: watchdog timeout" messages (which may be due
to hardware/cabling problems), "sendto: no buffer space
availble" messages (no idea where this comes from, any
hints appreaciated, kern.ipc.nmbclusters and kern.maxusers
etc, are bumped enough and did not max out (according
to netstat -m)).
So I thought, I run the production services on the reliable
xl0 and xl1 interfaces and assign a test IP address to the
lge0 interface, and if services from that interface run
reliable, too, I switch the others over, benefitting from
the increased bandwith.
Well, thats how I would like it to work. But it doesn't.
Is there any chance in FreeBSD to do it, and if, how?
I've heard some rumours, it is not possible to use multiple
NICs on the same subnet, since the IP stack would not know
which interface to use to transmit packets, since it could
not use its routing table (as the network is the same).
But my argument would be, of course it should use the
interface, which was configured with the address, the service
bound its source port to. If any service did bind to
IN_ADDR_ANY (0.0.0.0), the ip stack may choose the
default interface or just any interface to transmit the
packet from.
I've also heard Bill Paul did some work on fat ethernet channels,
which may be an implementation of Ciscos ethernet channel
trunking/bundling, which also requires support from the
switching counterpart. Although this is very interesting it
does not help me at all, since I do not intend to bundle
my NICs to a single fat channel, but to assign certain
services to it, and to do some testing, but all on
the same subnet.
Any help greatly appreciated.
Best regards,
Daniel
--
IRCnet: Mr-Spock - "I hear that, if you play the WindowsXP CD
backwards, you get a Satanic message!"
- "That's nothing. If you play it forward, it installs WindowsXP!"
Daniel Lang * dl@leo.org * +49 89 289 25735 * http://www.leo.org/~dl/
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